The present invention relates to an image sensor free from undesirable incident light rays which have not been reflected in the surface bearing the image to be sensed.
Along with the efforst to decrease the sizes of facsimile machines, photo-copying machines and the like, contact image sensors, as a very small photo-electric conversion sensor, have attracted interest of the researchers.
A couple of examples of conventional image sensors are illustrated in FIGS. 1(A) and 1(B). The sensor structure of FIG. 1(A) comprises a glass substrate 1, a front light blocking electrode 2, a photosensitive semiconductor film 3, a rear transparent electrode 4, and a transparent protector layer 5 which is to make direct contact with an original 6. A light window 7 is opened in the photoelectric conversion structure consisting of the electrodes 2 and 3 and the semiconductor film 5. Light rays 8 passed through the light window 7 are reflected by the original 6 and absorbed by the semiconductor film 3 with the visual information contained in the original 6.
Since the photoelectric conversion structure is formed by scribing the triple-layered laminae consisting of the electrodes 2 and 4 and the semiconductor film 3, there is a chance of forming short current paths across the opposed electrodes 2 and 4 during the simultaneous scribing. The sensor illustrated in FIG. 1(B) is constructed as similar to the structure of FIG. 1(A) except that a metallic electrode 9 is deposited on the semiconductor film 3 after scribing the underlying semiconductor film 3 and the light blocking electrode 2. The formation of short current paths between the electrodes 9 and 2 is unlikely in this case. This case, however, requires a fine patterning technique capable of fabricating comb electrode structures with adjacent conductive lines separated by several microns intervals.
Furthermore, in either case, it is evitable to suffer from the noise originating from the light rays which are inadvertently obliquely incident to the semiconductor film from its side surface 13. These undesirable light rays can produce carriers independent of whether the original 6 is white or black, and therefore reduce the quality of the copy.